Reverse DNS

DNS underpins so much of what the internet does – we would never be able to use the internet as easily as we do if it was not for the domain name system, or DNS. This is because DNS is the tool that translates an easy to remember domain name into a server IP address that can easily be handled by a server. Assigning a specific DNS record to a specified domain is called forward DNS, which is what leads a domain to the server IP. There is a process that does the opposite, going the other way. It’s called reverse DNS.

So, reverse DNS simply does this: it translates a specified IP address into a domain or hostname. It is the opposite of the forward domain resolution process. Reverse DNS is often called reverse DNS lookup but it also locates which hostname or domain belongs to a specific IP address. If an IP has a reverse DNS that is valid, typing it into your browser address bar will redirect you to the domain name associated with the IP.

You might ask why exactly one would need a reverse DNS set up for a server. Strictly speaking you will be fine using only a forward DNS, but in reality you are more likely to guarantee a solid uninterrupted service on the internet if you also set up a reverse DNS.

The reasons for this is mainly technical, but reverse DNS ensures that enterprise management, SMTP servers, network backup and r-commands all function smoothly. It’s also worth noting that reverse DNS is a key requirement for certain internet protocols. Finally, reverse DNS is also used by email spam processors that can check whether the IP address of an inbound email really matches the authenticated domain, blocking messages if there is a mismatch.